1M; KOH中Ag-Cu、Ag-Co二元薄膜觸媒對氧還原之催化 Catalytic activity of Ag-Cu and Ag-Co films for oxygen reduction reaction in 1M potassium hydroxide solution

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题名:	1M;KOH中Ag-Cu、Ag-Co二元薄膜觸媒對氧還原之催化 Catalytic activity of Ag-Cu and Ag-Co films for oxygen reduction reaction in 1M potassium hydroxide solution
作者:	張書維;Shu-Wei Chang
贡献者:	材料科學與工程研究所
关键词:	氧還原反應;慢速極化掃瞄;循環伏安法;Oxygen reduction reaction;Slow scan voltammetry
日期:	2007-06-21
上传时间:	2009-09-21 11:28:46 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本論文利用磁控濺鍍方式製備不同成分比例的薄膜觸媒，利用電化學實驗，包含慢速極化掃瞄、循環伏安測試、旋轉電極測試等配合光電子能譜儀分析結果探討Ag-Cu和Ag-Co二元薄膜觸媒在1M KOH鹼性溶液中成分比例與氧還原(Oxygen reduction reaction, ORR)活性之間的關係。慢速極化掃描結果可知：Cu和Co添加至Ag形成雙元薄膜電極，有助於提升其氧還原之催化活性，當Cu和Co濃度由10%增加至50%時，氧還原的催化活性越好。若比較Ag-Cu和Ag-Co兩種二元薄膜系統，Ag-Co系統的氧還原起始電位(0.179V)較Ag-Cu(0.089V)高，還原極限電流(-3.89mAcm-2)也較大，顯示Ag-Co二元薄膜系統對氧還原的催化效率較高。循環伏安測試結果顯示：在Ag-Cu二元薄膜系統中若Cu濃度增高，則氧化物的還原峰會往負電位偏移，使Ag-O鍵結較強，因而導致O2中O-O之間的鍵結較易斷裂，此為Ag-Cu二元系統中Cu濃度增加會增進活性的可能原因；而Ag-Co二元系統中Co的濃度增加同樣也會使陰極峰向負電位偏移，但偏移大小不如Ag-Cu二元系統。經由旋轉電極測試結果，配合Koutecky-Levich equation計算，結果顯示：Ag-Co系統中Co有助於催化包含四個電子的氧還原電極反應；而Ag-Cu系統則對於氧還原反應催化之電子數包含兩個電子，電子轉移數的差異顯示Ag-Co活性性較Ag-Cu佳。 XPS分析結果顯示：Ag-Co與Ag-Cu二元薄膜系統中銀金屬之含量與催化活性有密切關係，Ag-50Co中金屬Ag的比例較高，大約佔了70%以上，而Ag-50Cu中金屬Ag則佔約略55%左右，由先前Tafel實驗可知雙元金屬的活性中心為Ag，由於Ag-50Co中Ag的氧化物比例較低進而使活性面積比Ag-50Cu來的高，這可能是Ag-Co活性測試結果比Ag-Cu佳的原因。 Catalytic activity of Ag-Cu and Ag-Co films for oxygen reduction reaction (ORR) in KOH electrolyte was investigated in this work. Magnetron sputtering method was employed to prepare of Ag-Cu and Ag-Co thin films with different compositions. The dependence of the catalytic activity on the film composition was explored by means of the electrochemical techniques such as slow scan voltammetry(SSV), cyclic voltammetry(CV) and rotating disk electrode(RDE) with the aid of surface analysis of the films by x-ray Photoelectron Spectroscopy(XPS). Resulting from SSV, it was found that the catalytic activity of Ag-Cu and Ag-Co films for ORR increases with increasing the concentration of Cu (10, 30, 50 at%) and Co (10, 30, 50 at%) in the films. The onset potential (0.179V) of Ag-Co is higher and more closely to the ideal equilibrium potential for ORR than that (0.089V) of Ag-Cu. The limiting current of reduction is higher for Ag-Co (-3.89mAcm-2) than Ag-Cu (-2.87mAcm-2). Thus the catalytic activity of Ag-Co films is better than that of Ag-Cu for ORR According to cyclic voltammogram, the reduction peak of silver oxide is at lower potential for the Ag-Cu films compared to pure Ag film. This phenomenon indicates a stronger adsorbed-oxygen interaction with the Ag in Ag-Cu films than that in monotonic Ag-films. This stronger interaction between oxygen and silver facilitates the splitting of O-O bond thus increasing the ORR kinetics. There is also a shift of the reduction peak of silver oxide to lower potentials for the Ag-Co, however, less extent is this shift. The number of electron transfer involved in an electrochemical reaction was estimated by fitting the RDE data into the Koutecky-Levich equation. It was calculated that almost four electrons transferred in the process of ORR on Ag-Co films. Less number (about three) of electrons transferred was found on the Ag-Cu films. This difference reflects that the catalytic activity is better for Ag-Co than Ag-Cu. Analysis of XPS indicated that the catalytic activity of Ag-Cu and Ag-Co films decreases with increasing the percentage of silver oxide in the composition of the surface film. Higher percentage of silver oxide in Ag-Cu than Ag-Co leads to lower activity for the ORR.
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